Propagation Of Band-limited Spiral Modes In Turbulent Media

With the development of society,humanity have placed higher demands on the capacity,speed,confidentiality and accuracy of optical information transmission.In theory,the orbital angular momentum has the potential and prospect of carrying infinite dimensional degrees of freedom and greatly improving the channel capacity of the communication system.In the field of free optical communication,turbulent medium affects the transmission of orbital angular momentum carried by the beam.Therefore,it is important to study the influence of turbulent medium on the orbital angular momentum mode transmission law,especially the turbulent versus non-diffracting beam.The influence of the orbital angular momentum mode transmission is a research hotspot.However,the existing research ignores the diffraction effect of the beam edge,and the research results must be deviated from the actual situation.The main goal of this paper is to study the effect of beam diffraction on the orbital angular momentum mode transmission.Considering different fluids and different geographical environments,the corresponding turbulence has different laws.The influence of the diffraction of the beam edge on the orbital angular momentum mode transmission is reflected in the following two aspects: A: Influence of marine-atmosphere turbulence on the transmission of the orbital angular momentum mode of Bessel Gaussian vortex beamThe diffraction effect of the beam edge affects the transmission of the orbital angular momentum model carried by the vortex beam.Based on the bandwidth-limited orbital angular momentum orthogonal vortex,the influence of the weak Kolmogorov marine-atmosphere turbulence and the weak to strong non-Kolmogorov marine-atmosphere turbulence on the orbital angular momentum mode carried by Bessel Gaussian beam is studied.The theoretical models have been given.The content is as follows:a)The crosstalk probability of the optical orbital mode obtained by the bandwidth-limited probability model is greater than the crosstalk probability calculated by the helical plane model;the crosstalk probability of the bandwidth-limited optical orbital mode decreases with the increase of the internal scale of the turbulent flow.However,it increases with the increase of the external scale of turbulence;b)The crosstalk energy of the orbital angular momentum model carried by the Bessel Gaussian beam mainly diffuses to the nearest energy state;c)Small-value turbulence non-Kolmogorov exponent,small-value turbulent internal scale,producing large orbital angular momentum intermodal crosstalk;d)In the turbulent atmosphere,the transmission quality of the orbital angular momentum mode is improved by selecting a small initial amplitude radius beam,a low orbital momentum quantum number and a long wavelength of light.B: Influence of anisotropic ocean turbulence on the transmission of orbital angular momentum mode carried by partially coherent modified Bessel-related vortex beamsThe influence of anisotropic turbulence on the orbital angular momentum model carried by the coherent modified Bessel-dependent Gaussian beam in the ocean turbulence is studied.The received power model of the bandwidth-limited optical orbital angular momentum module in the paraxial link is established.The content is as follows:a)In the strong undulations of salinity,small-scale turbulence is an important factor affecting the transmission of the bandwidth-limited orbital momentum model;b)By selecting the small-value optical orbital angular momentum quantum number,the signal optical orbital angular momentum can be transmitted more efficiently,and multi-channel communication can be realized by selecting a large number of sub-number difference optical orbital angular momentum modules.